The Reserchement On Measurement Of Composite Materials Coating Thickness

Carbon fiber composite materials are among the most important aerospacialcomponents.However, these kinds of composite materials are easily to become ablatedand oxidated.Therefore,a layer of sic coating material with a thickness of approximate50～160μ m must be applied to prevent them from malfunction.In view of thesignificance of ascertaining the thickness of coatings in security of aerospacialcomponents, therefore the method of eddy-current test is the optimum way to measurenondestructively the ultrathin coating with a thickness of dozens ofμm.Aiming at the feature of the special carbon fiber composite material, the author hasused particular conductivity meter to measure the electroconductibility of thecomposite materials and coatings, so as to simulately analyze the possibility ofmeasuring the thickness of carbon fiber coatings by the lift-off-effect in theory, thenanalyze to what degree the measurement results are influenced by inhomogeneity ofthe electroconductibility.Afterwards,according to the characteristic of eddy currentsignals when the thickness of coating changes,the author has come up with a plan tooptimize the excitation parameters of eddy current system.Result of the simulationanalysis shows that,in the process of thickness measurement by eddy-current testmethod, adopting proper parameters can help to eliminate the influence of theinhomogeneity of electroconductibility to a large extent. To be specific, with properdetecting parameters, there appears a fine relavance and sensitivity between theimpedence of probes of testing coils and the thickness of the sic coatings on compositematerials. In this sense,the simulation analysis has provided a reliable theoreticalevidence for the eddy-current test in measuring the thickness of the sic coatings.On the basis of simulation analysis, the author has conducted a SEM measurementtest in the briquette sections of the existing composite materials, to get the acurate dataof the thickness of the destructive sectional coating so as to provide experimental basisfor the comparison of eddy-current test results.Meanwhile,the author has carried outexperiments to verify the result of theoretical analysi by testing the thickness of siccoatings of the base of composite materials.Then the author can ascertain thetheoretical measurement accuracy and measuring rage by conducting the simulationanalysis by other similar thin-film materials.At last, the conclusion of test has demonstrated the feasibility of the eddy-current test in the thickness measurement ofthe sic coatings on the composite materials.